Chemical energy
	High efficiency Few pollutants
Mechanical energy

The diesel engine's task is to convert the chemical energy, embedded in a very ignition-willing fuel, as efficiently as possible and with few emissions into mechanical energy.

Pure air is sucked in. Without supercharging a minimum compression of 18 : 1 is necessary for the combustion. (approx. 30 bar) The fuel is injected into the heated air. This takes place with a nozzle opening pressure of around 130 bars for the outdated side combustion chamber process, making use of the modern direct injection method substantially higher pressures are in place. Without electric ignition system the combustion occurs immediately (self-ignition). The injection pressure is generated by a mechanical high-pressure pump and through nozzles, reaches the combustion chamber.

In contrast to the petrol engine there is always more than enough air in all operational stages, also without supercharging. Therefore, and because of the high temperatures nitrogen oxides (NOX) tent to develop more easily. The shorter mixture formation and the approx. 13% higher C concentration in the diesel fuel in comparison to petrol fuel raises also the ejection of soot (particles). The diesel engine stands at the beginning of its exhaust gas cleaning program, the petrol-driven cars surpassed this stage already.